PAH when reduced, reacts with NO. The EPR, extending from g = 4 to g = 2 is indicative of an S = 3/2 system. The cw EPR is perturbed by either substrate or pterin addition. ESEEM studies show weak modulations from 14N that disappear in samples that are allowed to anneal. Studies to be carried out will be addressed at demonstrating interaction with substrate and/or cofactors using deuterated materials.